Take a look at the quantity - you requested quantity of 4 (all available items) and won them for 63.44. The bidder whose bid was 20.03 offered this amount for only one item (and lost).

I yet have to figure out how ebay came with this exact amount (63.44), and how proxy bidding works in dutch auctions, but to clarify - this calculation is not done by Gixen - Gixen submits your maximum bid, and then ebay takes over with proxy bidding.